The invention relates to a method of making fluid flow regulators in which passages are controlled by an elastically deformable ring, depending on the overpressure of the medium being controlled, which acts on said ring, thereby narrowing the passages.
Particularly the invention is related to a fluid flow regulator as specified in U.S. Pat. No. 3,847,178, issued Nov. 12, 1974.
As is described in that Patent, the various parts of the regulator, in particular the profiled core or the profiled inner wall of the casing, respectively, are preferably made as injection moulded plastic articles. The rate of flow through the regulator is determined by the size of the flow ports and thus by the shape of the protuberances. In this connection the protuberances may be of different height so that there are distinct main protuberances and lower supporting protuberances interposed therebetween.
It has been found in practice that the rate of flow through the regulator is extremely sensitive with respect to variations of the employed rings. The tolerances of these rings vary both with respect to dimensions and their elastic properties from one charge to the next so that, when large numbers are to be manufactured, there arises the problem of matching the casting moulds, which are also called injection cavities, to the respective charge of rings.
This means that a certain type of fluid flow regulator cannot be made with a single casting mould, i.e., a master mould, but that in the course of time a series of casting moulds has to be prepared and matched in such a way that the regulator made with the respective casting mould will have the predetermined desired flow value. Moreover, in the manufacture of the moulded parts the casting moulds are subject to wear and contamination so that their useful life is limited to the production of e.g. 50,000 castings. Thereafter, the tolerance variations of the moulded parts are so great that the flow characteristics of the regulators formed thereby deviate greatly from the desired value, so that a new casting mould will have to be used.
However, the making of such casting moulds poses a problem. The geometry of the profiled parts of the regulators is such that the corresponding casting moulds can hardly be made with cutting or milling machines so that preferably an electrical discharge machining method (EDM method), i.e., a spark erosion method or an electrolytic method, is employed. A casting mould made thereby cannot even by the use of an EDM method be produced with such accuracy that the moulded parts formed thereby result in a regulator having exactly the predetermined rate of fluid flow. The thus prepared casting mould is a "blank" of a casting mould and must therefore be matched and adapted such that the moulded parts taken therefrom result in a regulator exhibiting the predetermined desired value. For matching, the casting mould is changed so that the geometric configuration of one or several protuberances, i.e., of the main or the supporting protuberances, is changed. This is done, for instance, by cutting the casting mould with an abrasive diamond pencil.
Since the casting moulds made by means of EDM methods are relatively expensive, matching has to be performed very carefully so that the casting mould will not become useless due to excessive material removal. Therefore it has been necessary so far to finish-machine the casting mould with a large number of finishing steps and to make a sample after each single finishing step and measure the flow characteristic thereof, which is a time consuming and expensive process.
It is therefore the object of the present invention to provide measures by means of which the making of a fluid flow regulator of the above-specified type may be facilitated, and in particular to provide rules according to which a casting mould may be matched with the minimum number of machining steps in such a manner that the regulator parts produced thereby result in a regulator having the predetermined desired value for the fluid flow rate.